This invention relates generally to thin film inductive transducers, commonly referred to as thin film magnetic heads. These devices are useful for recording and reading magnetic transitions on a moving magnetic recording medium.
A thin film magnetic head generally has a basic construction in which a magnetic material layer is deposited on a substrate of magnetic material, with a conductor layer interposed therebetween. This substrate and magnetic material layer constitute a magnetic circuit, the rear end of the layer being magnetically connected to the substrate and the front end being magnetically separated from the substrate to form a recording gap. Electric current is caused to flow through the conductor for recording.
The magnetic reading and/or writing head must consist of the following essential parts, namely, a magnetic circuit having a magnetic discontinuity or "gap" with the terminations of the magnetic circuit on either side of the gap called the magnetic "pole pieces", and one or a number of electrical windings which surround the circuit and are intended to permit writing and/or reading. In order to take advantage of increased data packing densities on magnetic layers, it is essential that the gap and pole pieces be made to fine tolerances. In furtherance of this goal, it is most preferable that the pole pieces traveling in close proximity to the magnetic recording surface have straight, perpendicular side walls.
In those portions of the magnetic head assembly remote from the gap region, it is not advantageous to provide a structure having straight, perpendicular side walls. For example, the electrical windings, referred to above, surround the body of the head and their physical integrity would be greatly impaired by having to circumscribe straight, perpendicular walls.
In an article by Kelly and Koel entitled "Electrochemical Aspects of the Beveling of Sputtered Permalloy Films", J. Electrochem. Soc.:Eelectrochem. Science & Tech., Vol. 125, No. 6, pp. 860-65 (June, 1978), the production of thin film magnetic heads with beveled steps in sputtered permalloy films was taught. It was disclosed that a duplex layer comprising permalloy covered with titanium could be etched with an H.sub.2 SO.sub.4 /H.sub.2 O.sub.2 /HF etchant to produce a beveled surface whose bevel angle could be varied between 6.degree. and 40.degree., depending upon the concentration of the HF in the etchant.
Although the ability to bevel or slope the edges of a permalloy layer in producing a thin film head is useful as taught in the article cited above, it is recognized that a much more commercially important process would be one which could produce both variable sloped edges, as well as straight edges, in producing a thin film head. For example, it is important that the pole tip region of the thin film head be of critically reproducible proportions having straight edges for it is the pole tip region which flies proximate the magnetic recording media and failure on the part of the pole tips to exhibit finely controlled straight edges can result in read/write errors.
It is thus an object of the present invention to provide a method for producing variable sloped as well as straight edges on a permalloy thin film magnetic head.
It is yet another object of the present invention to provide a method for fabricating variable, as well as straight, edges on the permalloy body of a thin film head in a single series of chemical processing steps.